Transition sensing is one of the many sensor applications needed for automating food processing plants. Transition sensors determine the change from one product to another in a liquid piping system. Transition sensors that accurately determine the interface between product changes allow for more accurate control over processes to ensure product quality, reduced waste in food processing plants, and increased food safety. For example, in a typical pasteurization system, water is re-circulated through the pasteurizer while the temperature is rising to the pasteurization temperature. Once the desired temperature is reached, operators manually divert the flow of water to a drain line and open a valve to allow raw milk to chase the water through the pasteurizer. Operators use stopwatches to determine the time it takes for all the water to pass through the system. At the end of the “specified time”, they divert the fluid flow from the drain line to the process line. The “specified time” is not always accurate and the operators are occasionally late in manually diverting the product, resulting in product loss and an increase in effluent loading.
Optical sensors are currently commercially available for this application but are limited because they typically operate for only one product and require calibration to this product in the plant. The currently available sensors are response-based transition sensors, i.e., the output signal is proportional to an optical response (reflectance or transmission), and the sensor output is based on the detection of a specific level of reflectance or transmission. These sensors require calibration in a food processing facility for operation. Response-based sensors are generally unsatisfactory for operations involving multiple products where the optical or physical properties differ significantly. A single response-based transition sensor has difficulty establishing process control set points for two optically different (e.g., high vs. low reflectance) fluids. Recalibration is required if the response of a product changes due to changes in fat/protein/sugar content of the liquid, aging of the light source, scratch on lenses, etc. The plant technical personnel must be keenly aware of these changes to keep the sensors operating properly.
A versatile time-based method was developed for use with an optical transmission sensor. This sensor system performs for multiple products and does not require plant calibration. This disclosure is based on the application of the developed method to a measured optical sensor. It should be apparent that the method could be applied to the measured response of other sensors such as conductivity, temperature, ionic strength, pH, refraction, sonic properties, etc. This technology can be applied for monitoring the fluid pipe flows in the food, beverage, dairy, bioprocess, and chemical process industries among others.